1. Field of the Invention
The present invention relates to a high frequency discharge type of a plasma generating apparatus. The plasma generating apparatus controls the charge-up of the surface of the substrate in the ion beam radiation in an ion beam radiation apparatus for radiating an ion beam onto a substrate to enforce an ion implantation processing.
2. Description of the Related Art
As a high frequency discharge type of a plasma generating apparatus is used to control the charge-up of the surface of the substrate, in JP-A-2002-324511 (see e.g., Paragraph 0031-0038, FIG. 1). There is disclosed a plasma generating apparatus ionizes gas within a plasma generating container by high frequency discharge to thereby generate a plasma and also discharges the plasma to the outside through a plasma discharge hole. And also, the plasma generating apparatus includes an antenna disposed within the plasma generating container for radiating a high frequency wave. And an antenna cover composed of an insulator for covering the whole of the antenna disposed within the plasma generating container.
The antenna cover prevents the plasma from contamination with the metal particles (that is, metallic contamination) that are discharged from the antenna when the antenna is sputtered with the plasma.
However, in some cases, when the plasma generating apparatus is operated for a long period of time (for example, several hundreds of hours˜several thousands of hours), the antenna cover may fuse in part and the antenna may be exposed in the fused area of the antenna cover. Then, the antenna may be exposed to the plasma. As a result, it occurs the metallic contamination of the plasma.
The following presumption may probably account for the above phenomenon. That is, standing high frequency waves are generated along the antenna within the plasma generating container, the electric field becomes greatest in the middle portion of the standing high frequency waves, and electrons and ions contained in the plasma are strongly accelerated toward the antenna. When the plasma generating apparatus is operated for a long period of time in the manner, owing to the sputtering of the electrons and ions, the antenna cover may be shaved in part and may be thereby fused.
Suppose that the antenna cover is fused in the manner, the conventional plasma generating apparatus does not include an apparatus for detecting such fused condition. When keeping on the operation of the plasma generating apparatus, the metallic contamination of the plasma occurs while an operator may not detect it. When such metallic contamination occurs once, the substrate may also be contaminated by using the present plasma generating apparatus of the ion beam radiating apparatus.